The present invention relates to new and useful improvements in electric resistance heating elements, particularly of the cartridge type. The following U.S. patents afford an understanding of the prior art as presently known by applicants:
______________________________________ 2 831 951 Desloge Apr 22, 1958 2 977 453 Wells Mar 28, 1961 3 134 956 Boggs May 26, 1964 3 217 279 Boggs Nov 9, 1965 3 307 135 Simmons Feb 28, 1967 ______________________________________
The above noted patents, with the exception of Wells, disclose development of cartridge heater construction wherein ceramic cores, upon which resistance wires have been wound, are disposed in "skewered" relation on a pair of terminal pins or rods. Boggs U.S. Pat. No. 3,217,279 discloses a development wherein two or more coils may be placed in an electric circuit whereby a part or all of the coils may be energized. Simmons discloses an arrangement wherein two or more coils may be disposed in a series electrical relation.
The foregoing constructions do not possess the ability to effect other circuit relationships, such as utilization of one voltage source to energize one coil, and a different voltage source to energize another coil. For example, through use of our improved construction, one voltage may be 120 volts whereas the other may be 12 volts, or a three-phase connection may be made between coils separately wound on three cores. Other variations will be apparent from the description which follows.
The improvement over the prior art is made possible by providing a plurality of openings in each of at least two ceramic cores, the openings extending longitudinally of each core. Three metal pins fit into respective openings in the cores and at least certain of the pins maintain the cores in serially disposed, longitudinally aligned relation. Each core has a resistance wire coiled about its exterior surface, with terminals at opposite ends of the core. One of the terminals of each resistance coil is electrically connected to one pin; the opposite terminal of one resistance coil is electrically connected to a second pin; and the opposite terminal of the other resistance wire is electrically connected to the third pin, whereby the said one pin serves as a common electrical connection for both resistance coils, and the second and third pins serve as separate electrical connections to respective resistance coils. Thus, for example, the common pin may be connected to one terminal of a 120 volt source and to one terminal of a 12 volt source. The other terminal of the 120 volt source may be connected to the second pin and the other terminal of the 12 volt source may be connected to the third pin. By suitable switching arrangement, either one of the resistance coils may be energized. The particular example just mentioned has considerable utility for use as a heating device in a boat or automobile, where a 120 volt source is usually available when the auto is garaged, or the boat docked, but where only a 12 volt source is otherwise available.